As reported by Mother Jones:
You see, starting in about 2009, in the pits that capture manure under factory-scale hog farms, a gray, bubbly substance began appearing at the surface of the fecal soup. The problem is menacing: As manure breaks down, it emits toxic gases like hydrogen sulfide and flammable ones like methane, and trapping these noxious fumes under a layer of foam can lead to sudden, disastrous releases and even explosions. According to a 2012 report from the University of Minnesota, by September 2011, the foam had "caused about a half-dozen explosions in the upper Midwest…one explosion destroyed a barn on a farm in northern Iowa, killing 1,500 pigs and severely burning the worker involved."...The agriculture industry and the antibiotic producers seem to be fused at the hip.
But if the causes of manure foam remain a mystery, a solution seems to be emerging, Jacobson told me: Dump a bit of monensin, an antibiotic widely used to make cows grow faster, directly into the foam-ridden pit. At rather low levels—Jacobson told me that about 25 pounds of the stuff will treat a typical 500,000 gallon pit—the stuff effectively breaks up the foam, likely by altering the mix of microbes present. No other treatment has been shown to work consistently, he said.
(The video is a Vimeo one that seems not to embed or load well. There are pix at this PowerPoint presentation).